Well, that really was a can of worms.
I suppose if anyone harmed my kid (or probably any of the kids I know) I would want to find them and do them serious harm - in fact, given the chance there is a high probability that I would actually do it. However, that doesn't make it right, and that's why we have (in theory at least) impartial arbiters of justice in the form of the courts etc.

At the moment only a forensic psychologist can really tell us if this was a revenge attack, but I doubt it. More likely it's the work of a bunch low lives who've seen the chance to take out all the frustrations of their sh*tty existence while making themselves feel morally superior for perhaps the first time in their lives.